What Are the Lunar Nodes?
The first thing to understand is that the lunar nodes aren't planets, stars, or physical objects at all. They're points in space — specifically, the two places where the Moon's orbit around the Earth crosses the apparent path the Sun travels across the sky (the ecliptic).
The Moon's orbit is tilted slightly relative to that path, so it crosses it twice each cycle: once heading north, once heading south. Those two crossing points are the North Node and the South Node. They're always exactly opposite each other, and because of the mechanics of the Moon's orbit, they drift slowly backward through the zodiac, completing a full loop roughly every 18.6 years.
These same points are what make eclipses possible — eclipses only happen when a New or Full Moon lands near a node — which is part of why astrological tradition has long treated the nodes as points of fate, destiny, and significant turning. You don't need to take the mythology literally, though, for the nodal axis to be a strikingly useful lens on your life.